Image forming apparatus

ABSTRACT

An image forming apparatus is provided. The image forming apparatus includes an image forming unit configured to form a mark, a conveyance member configured, to convey the mark, a sensor configured to read the mark conveyed by the conveyance member, a measurement unit configured to measure a moving time period between a time when the image forming unit forms the mark and a time when the mark conveyed by the conveyance member is read by the sensor, and a determination unit configured to determine whether a traveling speed of the conveyance member is appropriate based on the moving time period measured by the measurement unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No.2010-287388, filed on Dec. 24, 2010, the entire subject matter of whichis incorporated herein by reference.

TECHNICAL FIELD

Aspects of the present invention relate to an image forming apparatus,and particularly, to an image forming apparatus having a conveyancemember that conveys an image.

BACKGROUND

There has been known an image forming apparatus which has a conveyancemember that carries and conveys a sheet or an image, such as a sheetconveyance belt that conveys a sheet toward an image forming part (forexample, which is an image transfer unit for an electro-photographictype or an ink ejection unit for an inkjet type) or an image conveyancebelt that conveys an image transferred from an image forming unit.According to the image forming apparatus, in order to perform a highquality printing, it is necessary to control a traveling speed of theconveyance member to be a target speed.

For example, JP 2006-178374A describes an image forming apparatus whichemploys a technique of controlling the traveling speed of a sheetconveyance belt to be constant. Specifically, in the image formingapparatus, in order to adjust the traveling speed of the sheetconveyance belt, marks provided on the sheet conveyance belt are readand feedback control is performed so that a detection interval of themarks becomes constant. Thereby, the traveling speed of the sheetconveyance belt is controlled to be a target speed.

However, that image forming apparatus has the following problems. Thatis, according to that image forming apparatus, in order to determinewhether the traveling speed of the sheet conveyance belt is appropriate,it is necessary to read the marks for traveling speed detection, whichare provided in advance at end portions of the sheet conveyance belt inthe width direction, and to detect a time interval between the adjacentmarks. However, when there is a scratch or foreign material in any ofthe adjacent marks, the time interval cannot be accurately measured.Therefore, it is possible to erroneously determine whether the travelingspeed is appropriate or whether the traveling speed is appropriatecannot be determined, so that the reliability is rather low.

SUMMARY

Accordingly, it is an aspect of the present invention to provide animage forming apparatus having high reliability of determining whether atraveling speed of a conveyance member is appropriate.

According to an illustrative embodiment of the present invention, thereis provided an image forming apparatus comprising: an image forming unitconfigured to form a mark; a conveyance member configured to convey themark; a sensor configured to read the mark conveyed by the conveyancemember; a measurement unit configured to measure a moving time periodbetween a time when the image forming unit forms the mark and a timewhen the mark conveyed by the conveyance member is read by the sensor;and a determination unit configured to determine whether a travelingspeed of the conveyance member is appropriate based on the moving timeperiod measured by the measurement unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will become moreapparent and more readily appreciated from the following description ofillustrative embodiments of the present invention taken in conjunctionwith the attached drawings, in which;

FIG. 1 is a block diagram showing an electrical configuration of an MFP;

FIG. 2 shows a schematic configuration of an image forming unit of theMFP shown in FIG. 1;

FIG. 3 shows a schematic configuration of a process unit of the MFPshown in FIG. 2;

FIG. 4 shows an arrangement of mark sensors and an example of speeddetection marks;

FIG. 5 shows an example of a registration pattern for positionaldeviation adjustment;

FIG. 6 shows an example of a density pattern for density deviationadjustment; and

FIG. 7 is a flowchart showing a sequence of a belt speed adjustmentprocess.

DETAILED DESCRIPTION

Hereinafter, an image forming apparatus and an image forming systemaccording to illustrative embodiments of the present invention will bespecifically described with reference to the accompanying drawings. Inthe illustrative embodiments, a multi-function peripheral (MFP) is anexample of the image forming apparatus and has a color printingfunction.

[Configuration of MFP]

As shown in FIG. 1, an MFP 100 of this illustrative embodiment includesa control unit 30 having a CPU 31, a ROM 32, a RAM 33, an NVRAM(non-volatile RAM) 34, an ASIC 35, a network interface 36 and a FAXinterface 37. In addition, the control unit 30 is electrically connectedto an image forming unit 10 that forms an image on a sheet, an imagereading unit 20 that reads an image of a document and an operation panel40 that displays an operation status and receives an input operation bya user.

The CPU 31 (an example of the measurement unit, the determination unit,the change unit and the adjustment unit) executes operations forimplementing various functions such as an image reading function, animage forming function, a FAX data transmission/reception function and abelt speed adjustment function that will be described later, in the MFP100, and is a center of control. The ROM 32 stores therein variouscontrol programs for controlling the MFP 100, various settings, initialvalues and the like. The RAM 33 is used as a work area from which thevarious control programs are read out or a storage area that temporarilystores image data. The NVRAM 34 is a non-volatile storage means and isused, as a storage area that preserves various settings, image data andthe like.

Based on the control programs read from the ROM 32 or signalstransmitted from various sensors, the CPU 31 controls the respectiveelements of the MFP 100 (for example, controls a turn-on timing of anexposure device configuring the image forming unit 10, driving motors ofvarious rollers configuring a conveyance path of a sheet) through theASIC 35 while storing results of the processing in the RAM 33 or NVRAM34.

The network interface 36 is connected to a network and enablesconnection with the other information processing apparatuses. The FAXinterface 37 is connected to a telephone line and enables connectionwith a FAX apparatus of another party. In the meantime, it is possibleto perform data communication with an external apparatus through thenetwork interface 36 or FAX interface 37.

[Configuration of Image Forming Unit of MFP]

Next, a configuration of the image forming unit 10 of the MFP 100 isdescribed with reference to FIG. 2. The image forming unit 10 has aprocess unit 50 that forms a toner image by an electro-photographicmethod and transfers the toner image on a sheet, a fixing device 8 thatfixes unfixed toner on the sheet, a sheet feeding tray 91 that storestherein sheets before image transfer and a sheet discharge tray 92 thatreceives thereon the sheets after the image transfer. The image readingunit 20 is provided above the image forming unit 10.

The image forming unit 10 has an exposure device 53 that illuminateslight to respective process units 50Y, 50M, 50C, 50K, a conveyance belt7 that conveys a sheet toward transfer positions of the respectiveprocess units 50Y, 50M, 50C, 50K and a mark sensor 61 that detects amark formed on the conveyance belt 7.

The image forming unit 10 has a conveyance path 11 (dashed-dotted linein FIG. 2) having a substantially S-shape so that the sheet stored inthe sheet feeding tray 91 provided at a bottom passes through a feederroller 71, registration rollers 72, the process unit 50 and the fixingdevice 8 and is then guided to the sheet discharge tray 92 through sheetdischarge rollers 76.

The process unit 50 can form a color image and have the process unitscorresponding to respective colors of yellow (Y), magenta (M), cyan (C)and black (K) arranged in parallel. Specifically, the process unit 50has the process unit 50C that forms an image of C color, the processunit 50M that forms an image of M color, the process unit 50Y that formsan image of Y color, and the process unit 50K that forms an image of Kcolor. The respective process units 50C, 50M, 50Y, 50K are arranged at apredetermined interval in the conveyance direction of the sheet.

FIG. 3 shows a configuration of the process unit 50K. The process unit50K has a photosensitive member 1 (an example of the conveyance member)having a dram shape, a charging device 2 that uniformly charges asurface of the photosensitive member 1, a developing device 4 thatdevelops an electrostatic latent image by toner, a transfer device 5that transfers a toner image on the photosensitive member 1 to the sheetand a cleaner 6 that electrically collects the toner (transfer remainingtoner) remaining on the photosensitive member 1 after the transfer fromthe surface of the photosensitive member 1. The photosensitive member 1and the transfer device 5 are arranged to contact the conveyance belt 7.The photosensitive member 1 opposes the transfer device 5 with theconveyance belt 7 being interposed therebetween. The process units 50C,50M, 50Y have the same configuration as that of the process unit 50K.

In each of the respective process units 50C, 50M, 50Y, 50K, the surfaceof the photosensitive member 1 is uniformly charged by the chargingdevices 2. Thereafter, the photosensitive member 1 is exposed by lightfrom the exposure device 53, so that an electrostatic latent image of animage to be formed on the sheet is formed thereon. Then, toner issupplied to the photosensitive member 1 through the developing device 4.Thereby, the electrostatic latent image on the photosensitive member 1becomes a visible image as a toner image.

The image forming unit 10 picks up a sheet stored, in the sheet feedingtray 91 one by one and conveys the sheet onto the conveyance belt 7.Then, the image forming unit 10 transfers the toner image formed in theprocess unit 50 onto the sheet. At this time, for a case of a colorprinting, toner images are formed by the respective process units 50Y,50M, 50C, 50K and are then overlapped on the sheet. In the meantime, fora case of a black-and-white printing, a toner image is formed only bythe process unit 50K and is then transferred onto the sheet. Thereafter,the sheet on which the toner images are transferred is conveyed towardthe fixing device 8, and the toner images are then heat-fixed on thesheet. Then, the sheet after the fixing is discharged to the sheetdischarge tray 92.

The conveyance belt 7 (an example of the conveyance member) is anendless belt that is wound around conveyance rollers 73, 74 and is madeof resin material such as polycarbonate and the like. The conveyanceroller 73 on which the conveyance belt 7 is wound is urged in adirection of separating away from the conveyance roller 74. Thereby, theconveyance belt 7 tightly extends over the conveyance roller 73 and theconveyance roller 74. It is noted that the conveyance belt 7 may bestretched by thermal expansion. When the conveyance belt 7 is stretched,the conveyance belt 7 is stretched in the more upstream side from theprocess unit 50 by the conveyance roller 73 that is urged in thedirection of separating away from the conveyance roller 74.

The conveyance roller 74 is a driving roller that is driven by a drivingmotor 75. As the conveyance roller 74 is rotated, the conveyance belt 7is rotated in a counterclockwise direction. Thereby, the sheet that isput on the conveyance belt is conveyed from the registration rollers 72toward the fixing device 8. The conveyance roller 73 is rotated as theconveyance belt 7 is moved.

The mark sensor 61 is provided downstream from the process units 50Y,50M, 50C, 50K and upstream from the fixing device 8 with respect to theconveyance direction of the sheet. The mark sensor 61 detects marks thatare formed by the process units 50C, 50M, 50Y, 50K and are transferredonto the conveyance belt 7.

Specifically, as shown in FIG. 4, the mark sensor 61 includes twosensors, i.e., a sensor 61R that is arranged at a right side of theconveyance belt 7 in a width direction and a sensor 61L that is arrangedat a left side thereof. Each of the sensors 61R, 61L is areflection-type optical sensor having a pair of a light emitting device62 (for example, LED) and a light receiving device 63 (for example,photo transistor). The mark sensor 61 illuminates light onto the surface(dotted ranges E in FIG. 4) of the conveyance belt 7 in an obliquedirection by the light emitting devices 62 and receives the light by thelight receiving devices 63, respectively.

The marks 66 are formed by the respective process units 50C, 50M, 50Y,50K and transferred onto the conveyance belt 7. As the conveyance belt 7is rotated, the marks are conveyed in an arrow A direction of FIG. 4.The mark sensor 61 detects the mark by a difference between an amount ofreceived light when the mark 66 passes and an amount of received lightthat is directly received from the conveyance belt 7.

As shown in FIG. 4, the marks 66 are respectively formed by the processunits 50C, 50M, 50Y, 50K. Specifically, the mark that is formed by theprocess unit 50K is referred to as the mark 66K, the mark that is formedby the process unit 50C is referred to as the mark 66C, the mark that isformed by the process unit 50M is referred to as the mark 66M, and themark that is formed by the process unit 50Y is referred to as the mark66Y. The marks 66K, 66C, 66M, 66Y are formed at the same time andtransferred at the same time. Accordingly, the intervals of the marks66K-66C-66M-66Y are the substantially same as those of the transferpositions of the process units 50C-50M-50Y-50K.

In addition, the respective marks 66K, 66C, 66M, 66Y are formed inplural. An image forming timing is adjusted so that the marks are notoverlapped with each other when transferring the marks onto theconveyance belt 7. That is, the marks 66 are formed at a constantinterval in the sub-scanning direction (moving direction of theconveyance belt 7 shown in FIG. 4).

In this illustrative embodiment, the respective marks 66K, 66C, 66M, 66Yhave a rectangular rod shape and are respectively arranged in parallelwith the main scanning direction (direction orthogonal to thesub-scanning direction, width direction of the conveyance belt 7). Forexample, by detecting the mark 66K by the mark sensor 61, there can bemeasured the time period (moving time period) between a time when themark 66K is formed by the developing unit 60K and a time when the mark66K is detected by the mark sensor 61. Since the mark 66 is dedicatedmark for measuring the moving time period, the mark 66 can be simplewhile considering reduction of toner consumption.

In the meantime, the mark that is detected by the mark sensor 61 is notlimited to the mark 66 for traveling speed measurement. For example, themark sensor 61 also reads a registration pattern that is a mark forpositional deviation adjustment. For example, as shown in FIG. 5, theregistration pattern 67 includes a pair of rod-shaped marks in which onemark 671 is parallel with the main scanning direction and the other mark672 is inclined with respect to the main scanning direction. In theregistration pattern 67, a degree of positional deviation in the mainscanning direction is specified by time period between a detectiontiming of the mark 671 to a detection timing of the mark 672 and adegree of positional deviation in the sub-scanning direction isspecified by non-uniformity of the time from the detection timing of themark 671 to the detection timing of the mark 672.

In addition, the mark sensor 61 may also read a density pattern that isa mark for density deviation adjustment. For example, as shown in FIG.6, the density pattern 68 has an image pattern in which a densitydifference is provided in the sub-scanning direction. Then, amounts ofreflected light from the density pattern 68 are detected. Based on theamount of reflected light, a density is specified.

Also, a waste toner box 78 for collecting the toner attached on theconveyance belt 7 is provided to contact the conveyance belt 7. Thewaste toner box 78 collects the transfer remaining toners dischargedfrom the cleaners 6 of the respective process units 50C, 50M, 50Y, 50Kand the mark 66 having passed to the measurement position E of the marksensor 61.

[Belt Speed Adjustment Process]

In the below, a belt speed adjustment process of acquiring a speed ofthe conveyance belt 7 and adjusting the speed (if necessary) isdescribed with reference to a flowchart of FIG. 7. The belt speedadjustment process is executed by the CPU 31 when a predeterminedcondition is satisfied. The predetermined condition may include, forexample, when a power supply turns on, when the printed number of sheetsfrom previous adjustment process reaches a threshold value or larger,when a change of temperatures from previous adjustment process is athreshold, value or higher, when elapsed time from previous adjustmentprocess is a threshold value or greater, when a user inputs aninstruction, and the like.

In the belt speed adjustment process, it is determined whether phases ofthe photosensitive member 1 and the conveyance belt 7 coincide with eachother (S101). The rotating member such as the photosensitive member 1,the conveyance belt 7 or driving roller 74 of the conveyance belt 7 hasperiodic speed non-uniformity due to eccentricity, seams and the like.Accordingly, in order to suppress the influence of the speednon-uniformity, the measurement is preferably made at similar conditionsas much as possible. Hence, when the phases of the photosensitive member1 and the conveyance belt 7 do not coincide with each other (S101: NO),the process stands by until the phases coincide. Regarding the phase,there are three phases i.e. the phase of the conveyance belt 7, thephase of the driving roller 74 and both phases and any phase may beadopted in the determination of S101.

When the phases of the photosensitive member 1 and the conveyance belt 7coincide with each other (S101: YES), the process units 50C, 50M, 50Y,50K respectively form the marks 66C, 66M, 66Y, 66K at the sametime(Si02). Thereafter, the marks 66C, 66M, 66Y, 66K are transferredonto the conveyance belt 7 at the same time and are conveyed as theconveyance belt 7 is rotated.

After S102, the mark sensor 61 detects the passing of the respectivemarks 66C, 66M, 66Y, 66K, so that the time period (moving time period)between a time of the image formations of the respective marks 66C, 66M,66Y, 66K and a time of the mark detections (S103).

Then, based on the moving time period acquired in S103, the travelingspeed of the conveyance belt 7 is calculated (S104). Specifically, thetraveling speed is calculated as explained below.

First, distances are defined as follows.

LC: distance from a transfer position of the process unit 50C to areading position of the mark sensor 61.

LM: distance from a transfer position of the process unit 50M to areading position of the mark sensor 61.

LY: distance from a transfer position of the process unit 50Y to areading position of the mark sensor 61.

LK: distance from a transfer position of the process unit 50K to areading position of the mark sensor 61.

LC, LM, LY and LK are design values and are stored in the ROM 32. Inthis illustrative embodiment, there are arranged in order of theprocessing units 50K, 50Y, 50M, 50C from the upstream side of the sheetconveyance direction, so that the relationship is LC<LM<LY<LK.

The moving time period is defined as follows. In the meantime, when aplurality of the marks 66 is formed for one color, an average value iscalculated.

T1C: moving time period, of mark 66C.

T1M: moving time period of mark 66M.

T1Y: moving time period of mark 66Y.

T1K: moving time period of mark 66K.

T1C, T1M, T1Y and T1K are values measured in S103. In this illustrativeembodiment, the time of image formation, which is a starting time of themoving time period, is the time of exposure. However, the time of imageformation is not limited to the time of exposure and may be time ofdeveloping or time of transfer.

T2C: time period from an exposure position of the process unit 50C to atransfer position.

T2M: time period from an exposure position of the process unit 50M to atransfer position.

T2Y: time period from, an exposure position of the process unit 50Y to atransfer position.

T2K: time period, from an exposure position of the process unit 50K to atransfer position.

T2C, T2M, T2Y and T2K are respectively calculated from an angle from anexposure position to a transfer position and an angular velocity of thephotosensitive member 1. As the angle and the angular velocity are used,the above time periods are not influenced by a change of a drum diameterdue to the temperature change.

T3C: time period (T1C-T2C) from a transfer position of the process unit50C to a reading position of the mark sensor 61.

T3M: time period (T1M-T2M) from a transfer position of the process unit50M to a reading position of the mark sensor 61.

T3Y: time period (T1Y-T2Y) from a transfer position of the process unit50Y to a reading position of the mark sensor 61.

T3K; time period (T1K-T2K) from a transfer position of the process unit50K to a reading position of the mark sensor 61.

Based on the above values, the traveling speed of the conveyance belt 7,which is calculated for a single mark of each color, is as follows(calculation method 1).V1C: LC/T3CV1M: LM/T3MV1Y: LY/T3YV1K: LK/T3K

It is noted that since it is possible to calculate the traveling speedby a single mark in the calculation of the traveling speed by thecalculation method 1, it is not necessary to calculate the travelingspeeds for all the four colors, and therefore, the mark may be formed byat least one color. However, the traveling speed calculated in thecalculation method 1 is more influenced by an error as the movingdistance is shorter. Accordingly, in the calculation method 1, it ispreferable to calculate the traveling speed V1K, in which the movingdistance to the mark sensor 61 is longest. That is, when it is intendedto acquire the traveling speed of the conveyance belt 7 by thecalculation method 1, at least the mark 66K is formed by the processunit 50K.

In addition, the traveling speed of the conveyance belt 7, which iscalculated based on the moving time period of marks of plural colors, isas follows (calculation method 2).V2=(V1C+V1M+V1Y+V1K)/4.

In the calculation method 2, since the marks of four colors are used, itis also possible to calculate color deviation in the sub-scanningdirection at the same time with the traveling speed by measuring adetection interval between the marks of respective colors.

Alternatively, the traveling speed of the conveyance belt 7, which iscalculated based on the moving time period of marks of respectivecolors, is as follows (calculation method 3).V3={4×(T3C×LC+T3M×LM+T3Y×LY+T3K×LK)−(T3C+T3M+T3Y+T3K)×(LC+LM+LY+LK)}/{4×(T3C² +T3M ² +T3Y ² +T3K ²)−(T3C+T3M+T3Y+T3K)²}

The calculation method 3 calculates the traveling speed by the leastsquare method. In the calculation method 3, the calculation processesare increased, compared to the calculation method 2. However, thecalculation method 3 has high precision and tolerance to the error.Also, since the marks of four colors are used, like the calculationmethod 2, it is also possible to calculate the color deviation in thesub-scanning direction at the same time with the traveling speed.

After calculating the traveling speed in S104, the moving time periodT1C, T1M, T1Y, T1K of the respective marks are stored in the NVRAM 34(S105). Then, it is determined whether a speed difference between areference speed V0 which is pre-stored in the ROM 32 and the travelingspeed which is stored at this time is a first threshold value or greater(S106).

It is noted that the reference speed V0 of the traveling speed of theconveyance belt 7 is a traveling speed that is obtained by performing atest of the traveling speed of the conveyance belt 7 under environmentswithin a predetermined temperature range before the shipment. Thereference speed can be acquired in the same sequence as S101 to S104.That is, the reference speed that is used in S106 is a value that isindividually set for each image forming apparatus.

When the speed difference is smaller than the first threshold value(S016: NO), it is determined that the traveling speed is within anappropriate range and it is not necessary to adjust the speed.Accordingly, the belt speed adjustment process ends without adjustingthe speed.

On the other hand, when the speed difference is the first thresholdvalue or greater (S106: YES), the traveling speed is beyond theappropriate range and it is thus necessary to adjust the speed.Therefore, the angular velocity of the driving motor 75 of theconveyance roller 74 is controlled to adjust the speed of the conveyancebelt 7 by feedback control so that the traveling speed approaches thereference speed V0 (S107).

Then, it is determined whether a speed difference between the travelingspeed stored at previous time and the traveling speed stored at thistime is a second threshold value or larger (S108). The second thresholdvalue is larger than the first threshold value. In S108, it isdetermined whether the speed difference is considerably increased. Whenthe speed difference is smaller than the second threshold value (S108:NO), the belt speed adjustment process ends.

On the other hand, when the speed difference is the second thresholdvalue or larger (S108: YES), this means that the speed difference isremarkably large. Thus, it is expected that the color deviation occursby a cause different from the traveling speed of the conveyance belt 7.Accordingly, the registration pattern 67 shown in FIG. 5 is formed(S109) and the registration pattern 67 is detected by the mark sensor61, thereby performing a positional deviation correction (S110). AfterS110, the belt speed adjustment process ends.

Specifically, in S110, a degree of color deviation is calculated and theexposure timing is adjusted based on the degree of color deviation. Thedegree of color deviation and the adjustment amount are calculated asexplained below, for example. First, distances between the developingunits and weight values are defined as follows.

LKC: distance between transfer positions of the process unit 50K and theprocess unit 50C.

LKM: distance between transfer positions of the process unit 50K and theprocess unit 50M.

LKY; distance between transfer positions of the process unit 50K and theprocess unit 50Y.α=LKC/LCβ=LKM/LMγ=LKY/LY

LKC, LKM, LKY, α, β and γ are design values and are stored in the ROM32.

In addition, a moving time period difference ΔT between a value ofprevious time and a value of this time is calculated as follows.

T0: moving time period measured at previous time (which is stored in theNVROM 34).

T1: moving time period measured at this time.

T2: moving time period from an exposure position to a transfer position.

T3: value of the previous time (T0−T2) of the time period from atransfer position to a reading position of the mark sensor 61.

T4: value of this time (T1−T2) of the time period from a transferposition to a reading position of the mark sensor 61.

ΔT: difference (T4−T3) between a value of previous time and a value ofthis time.

An assumed degree of color deviation and an adjustment amount ofreducing the color deviation are as follows.

V0: design value of the traveling speed of the conveyance belt 7 (whichis stored in the ROM 32).

degree of color deviation between K and C: V0×ΔT×α

degree of color deviation between K and M: V0×ΔT×β

degree of color deviation between K and Y: V0×ΔT×γ

adjustment amount of exposure timing between K and C=ΔT×α

adjustment amount of exposure timing between K and M=ΔT×β

adjustment amount of exposure timing between K and Y=ΔT×γ

As described above, in the MFP 100 according to the present illustrativeembodiment, when acquiring the traveling speed of the conveyance belt 7,the respective process units 50C, 50M, 50Y, 50K form the marks 66C, 66M,66Y, 66K and the moving time period by the mark sensor 61 reads therespective marks is measured. Then, the traveling speed of theconveyance belt 7 is acquired based on the moving time period of theindividual marks and it is determined whether the traveling speed isappropriate. That is, the determination target (traveling speed in thisillustrative embodiment) is acquired from the measurement result of asingle mark 66, which means that the determination target is notacquired from measurement results of a plurality of marks, as in therelated art. Accordingly, compared to the related art, there is a lowpossibility that an erroneous determination or determinationimpossibility will occur and the reliability of determining whether thetraveling speed of the conveyance belt 7 is appropriate improves.

In this illustrative embodiment, the traveling speed is acquired basedon the moving time period of the single mark, regardless of thedetection interval of the adjacent marks. Furthermore, even when theconveyance belt 7 is stretched, due to the thermal expansion, the movingdistance of the mark is not changed. Accordingly, the reliabilityimproves because the traveling speed is not influenced well by thestretching of the conveyance belt 7 accompanied with the temperaturechange.

While the present invention has been shown and described with referenceto certain illustrative embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

For example, the image forming apparatus is not limited to the MFP andthe inventive concept of the present invention may be applied any imageforming apparatus having a printing function such as printer, copier andFAX apparatus. In addition, the image forming apparatus is not limitedto the electro-photographic type and an inkjet method may be employed.For example, for the inkjet type, the time at which ink is ejected maybe the measurement start time of the moving time period. Further, theMFP 100 of the illustrative embodiment is a direct transfer tandem type.The inventive concept of the present invention may be also applied to anintermediate transfer type or four-cycle type.

In the above illustrative embodiment, the MFP having the color printingfunction is described. However, the image forming apparatus is notlimited to the color printing apparatus. For example, the inventiveconcept of the present invention may be also applied to ablack-and-white printing apparatus having only one process unit.

In the above illustrative embodiment, each of all the process unitsforms a plurality the marks 66 for speed measurement and the moving timeperiod of each mark is measured to calculate the traveling speed of theconveyance belt 7. However, the present invention is not limitedthereto. For example, the respective process units may form a singlemark 66. Alternatively, one process unit may form a plurality of marks66. Also, one process unit may form a single mark 66. By reducing thenumber of the marks 66, it is possible to suppress the consumption ofthe toner. On the other hand, by increasing the number of the marks 66,it is possible to improve the accuracy of the moving time period to bemeasured.

In the above illustrative embodiment, when acquiring the travelingspeed, the marks 66 are formed by all the process units 50C, 50M, 50Y,50K. However, as described above, some of the process units may form themarks. In this case, the longer the moving time period of the mark, theconsiderable error of the moving time period appears. Thereby, it ispossible to easily determine whether the traveling speed is appropriate.Accordingly, it is preferable to form the mark 66K by the process unit50K, which has the longest mark moving distance.

In the above illustrative embodiment, the mark 66 is formed in conditionthat the phases between the photosensitive member 1 and the conveyancebelt 7 coincide with each other. However, the present invention is notlimited thereto. For example, the mark 66 may be formed in conditionthat the phases between the photosensitive member 1 and the drivingroller 74 of the conveyance belt 7 coincide with each other. Also, it isnot necessarily required to match the phases of the two rotatingmembers. For example, the same phase may be used so as to initiate themark formation at the same position for one of the photosensitive member1, the conveyance belt 7 and the driving roller 74 of the conveyancebelt 7, so that it is possible to suppress the influence on the speednon-uniformity of the corresponding rotating member.

In the above illustrative embodiment, after the traveling speed of theconveyance belt 7 is calculated, it is directly determined whether thetraveling speed is appropriate. That is, since the moving distance ofthe mark is fixed, it may be possible to indirectly determine whetherthe traveling speed is appropriate by determining whether the movingtime period of the mark is appropriate.

In the above illustrative embodiment, when the current traveling speedof the conveyance belt 7 is beyond the appropriate range, the speed ofthe driving roller 74 of the conveyance belt 7 is adjusted. However, thepresent invention is not limited thereto. For example, it may bepossible to stop the moving of the conveyance belt 7 as determining thatan error occurs. Also, it may be possible to adjust the exposure timingto the current traveling time of the conveyance belt 7.

In the above illustrative embodiment, the speed difference between thetraveling speed and the reference speed. V0 that is the traveling speedat the shipment time is calculated. However, the present invention isnot limited thereto. For example, it may be possible that a speeddifference between the traveling speed measured at previous time and thecurrent traveling speed is calculated and it is determined whether thespeed difference is the first threshold value or larger.

In the above illustrative embodiment, the mark sensor 61 detects themark 66 for traveling speed measurement and the registration pattern 67for positional deviation (color deviation) adjustment and reads thedensity pattern 68 for density deviation adjustment. However, dedicatedsensors may be respectively provided. In the meantime, the mark sensor61 has the function of reading the plurality of types of marks, like theabove illustrative embodiment, so that it is possible to reduce thenumber of sensors.

In the above illustrative embodiment, the marks 66 for traveling speed,measurement are formed at both ends of the conveyance belt 7. However,the marks may be formed only at one end portion.

In the above illustrative embodiment, the CPU 31 performs the belt speedadjustment process or the like. However, the present invention is notlimited thereto and a plurality of CPUs or a special ASIC may performthe belt speed adjustment process or the like.

What is claimed is:
 1. An image forming apparatus comprising: an imageforming unit including a rotary member configured to form a mark; aconveyance member including an endless conveyance belt configured toconvey the mark; a sensor configured to read the mark conveyed by theconveyance belt; and a control device configured to perform: a phasedetermining process of determining whether a rotation phase of therotary member and a rotation phase of the conveyance belt coincide witheach other; an instructing process of instructing the image forming unitto form the mark when the phase determining process determines that therotation phase of the rotary member and the rotation phase of theconveyance belt coincide with each other; a reading process of causingthe sensor to read the mark which is formed by the image forming unitbased on the instructing process and conveyed by the conveyance member;a measuring process of measuring a time period from a time when theimage forming unit forms the mark based on the instructing process to atime when the sensor reads, in the reading process, the mark, which isformed by the image forming unit based on the instructing process andconveyed by the conveyance member; and a determining process ofdetermining whether a traveling speed of the conveyance member isappropriate based on the time period measured in the measuring process.2. The image forming apparatus according to claim 1, wherein a pluralityof image forming units are provided, and wherein the instructing processinstructs at least one of the image forming units, for which the timeperiod is to be longest, to form the mark.
 3. The image formingapparatus according to claim 1, wherein a plurality of the image formingunits are provided, wherein the instructing process instructs at leasttwo of the image forming units to form marks, respectively, and whereinthe determining process determines whether the traveling speed of theconveyance member is appropriate based on a plurality of time periodsmeasured for the respective marks.
 4. The image forming apparatusaccording to claim 3, wherein the instructing process instructs the atleast two of the image forming units to form the marks at the same time.5. The image forming apparatus according to claim 1, wherein thedetermining process uses a determination criterion for determiningwhether the traveling speed of the conveyance member is appropriate, andwherein the determination criterion is a value that IS set for eachImage forming apparatus.
 6. The Image forming apparatus according toclaim 1, wherein the control device is further configured to perform: achanging process of changing the traveling speed of the conveyancemember when it is determined that the traveling speed of the conveyancemember is not appropriate.
 7. The Image forming apparatus according toclaim 1, wherein the control device is further configured to perform: apositional deviation adjustment when it is determined that the travelingspeed of the conveyance member is not appropriate.
 8. The image formingapparatus according to claim 1, wherein the reading process furthercauses the sensor to read a mark, which is formed by the image formingunit and is an adjustment image for at least one of positional deviationand density deviation.
 9. An image forming apparatus comprising: animage forming unit configured to form a mark; a conveyance memberconfigured to convey the mark; a sensor configured to read the markconveyed by the conveyance member; and a control device configured toperform: an instructing process of instructing the image forming unit toform the mark; a reading process of causing the sensor to read the markwhich is formed by the image forming unit based on the instructingprocess and conveyed by the conveyance member; a measuring process ofmeasuring a time period from a time when the image forming unit formsthe mark based on the instructing process to a time when the sensorreads, in the reading process, the mark which is formed by the imageforming unit based on the instructing process and conveyed by theconveyance member; and a determining process of determining whether atraveling speed of the conveyance member is appropriate based on thetime period measured in the measuring process, wherein the mark is adedicated mark for measuring the time period and is different from amark for positional deviation adjustment and a mark for densitydeviation adjustment.
 10. An image forming apparatus comprising: aplurality of image forming units configured to form marks, respectively;a conveyance member configured to convey the marks; a sensor configuredto read the marks conveyed by the conveyance member; and a controldevice configured to perform: an instructing process of instructing oneof the image forming units, which is provided furthest from the sensor,to form the mark; a reading process of causing the sensor to read themark which is formed by the one of the image forming units based on theinstructing process and conveyed by the conveyance member; a measuringprocess of measuring a time period from a time when the one of the imageforming units forms the mark based on the instructing process to a timewhen the sensor reads, in the reading process, the mark which is formedby one of the image forming units based on the instructing process andconveyed by the conveyance member; and a changing process of changing atraveling speed of the conveyance member based on the time periodmeasured in the measuring process.
 11. An image forming apparatuscomprising: an image forming unit including a rotary member configuredto form a mark; a conveyance member including a driving roller and anendless conveyance belt which is driven by the driving roller andconfigured to convey the mark; a sensor configured to read the markconveyed by the conveyance belt; and a control device configured toperform: a phase determining process of determining whether a rotationphase of the rotary member and a rotation phase of the driving rollercoincide with each other; an instructing process of instructing theimage forming unit to form the mark when the phase determining processdetermines that the rotation phase of the rotary member and the rotationphase of the driving roller coincide with each other; a reading processof causing the sensor to read the mark which is formed by the imageforming unit based on the instructing process and conveyed by theconveyance member; a measuring process of measuring a time period from atime when the image forming unit forms the mark based on the instructingprocess to a time when the sensor reads, in the reading process, themark which is formed by the image forming unit based on the instructingprocess and conveyed by the conveyance member; and a determining processof determining whether a traveling speed of the conveyance member isappropriate based on the time period measured in the measuring process.12. The image forming apparatus according to claim 11, wherein aplurality of image forming units are provided, and wherein theinstructing process instructs at least one of the image forming units,for which the time period is to be longest, to form the mark.
 13. Theimage forming apparatus according to claim 11, wherein a plurality ofthe image forming units are provided, wherein the instructing processinstructs at least two of the image forming units to form marks,respectively, and wherein the determining process determines whether thetraveling speed of the conveyance member is appropriate based on aplurality of time periods measured for the respective marks.
 14. Theimage forming apparatus according to claim 13, wherein the instructingprocess instructs the at least two of the image forming units to formthe marks at the same time.
 15. The image forming apparatus according toclaim 11, wherein the determining process uses a determination criterionfor determining whether the traveling speed of the conveyance member isappropriate, and wherein the determination criterion is a value that isset for each image forming apparatus.
 16. The image forming apparatusaccording to claim 11, wherein the control device is further configuredto perform: a changing process of changing the traveling speed of theconveyance member when it is determined that the traveling speed of theconveyance member is not appropriate.
 17. The image forming apparatusaccording to claim 11, wherein the control device is further configuredto perform: a positional deviation adjustment when it is determined thatthe traveling speed of the conveyance member is not appropriate.
 18. Theimage forming apparatus according to claim 11, wherein the readingprocess further causes the sensor to read a mark, which is formed by theimage forming unit and is an adjustment image for at least one ofpositional deviation and density deviation.